A pressurized-water reactor has a reactor coolant system in which the necessary pressure is kept on the water, by being connected to a pressurizer. This is a vertical tank containing coolant in its lower part and pressurized gas in its upper part, the pressurized gas maintaining the necessary pressure on the coolant in the system.
Any sudden increase in the reactivity of the reactor can cause a sudden increase in the coolant pressure in the system, and, therefore, the pressurizer above its water level, is connected with a pressurizer relief or surge tank.
Such a relief or surge tank is also a tank partially filled with water and having a pressurized gas cushion above the water. During a coolant pressure surge, the pressurizer transfers the pressure increase from its coolant to its relief tank, and because of the pressure differential, the transfer is largely in the form of steam.
That steam is ordinarily radioactive to some degree and cannot be discharged directly to the atmosphere, it being the function of the relief tank to accept such steam. To do this, the relief tank must distribute the incoming steam within its water to condense the steam as much as possible to reduce the volume involved while providing for gas cushioning.
Heretofore, such a pressurized-water reactor coolant system pressurizer relief or surge tank has distributed the incoming steam through a large number of pipes and a number of distribution nozzles, arranged in the form of a Christmas tree. This has involved an undesirable construction and maintenance expense and necessitated the need for an undesirably large tank size.